Electron microscopy and conventional autoradiography will be used to study possible daily rhythms in three parts of the visual cell: the outer segment, the inner segment, and the nucleus. The processes to be studied are, respectively: disc shedding by cones (goldfish), exocytosis of membranes from visual cell inner segments (goldfish, frog), and RNA synthesis by rods and cones (goldfish). The overall objective is to test the idea that daily rhythms affect nearly all aspects of visual cell metabolism. Furthermore, it is suspected that many daily rhythms in rods will be about one-half day out of phase with respect to comparable daily rhythms in cones.